Continuing advances in medical science, and specifically in the field of radiation treatment, have allowed the development of more precise, targeted treatment options for patients with tumorous cells that results in less radiation being applied to healthy cells. However, for each of the two main types of radiation treatment, i.e. radiosurgery and radiotherapy, precise imaging of the tumor location is critical to ensure the radiation is delivered only to the target area. This is particularly important in radiosurgery because of the intense doses of radiation that are delivered to the patient are intended to destroy tumorous cells or otherwise treat the target region. While the amount of radiation delivered to a patient during radiotherapy is typically about an order of magnitude smaller than used in radiosurgery, for example to treat early stage cancers, precise delivery to the cancerous cells is still very important to minimize the negative impact on the patient. As such and for ease of understanding, the following description will use the term radiotherapy to refer to both radiosurgery and radiotherapy.
In each of these radiation treatment operations, it is necessary to determine with precision the location of the target region and surrounding critical structures relative to the reference frame of the treatment device. It is also necessary to control the position of the radiation source so that its beam can be precisely directed to the target tissue while avoiding surrounding healthy tissue, with control of propagation in and through other body structures.
To effect such beam position control, frameless stereotactic radiotherapy systems have been developed, which implement image-guided radiotherapy using a robot. An image-guided robotic system provides the requisite beam position control for accurate delivery of therapeutic radiation, while eliminating the need for rigid stereotactic frames. Such image-guided robotic systems typically include a treatment beam generator mounted onto a robot and a controller. The treatment beam generator provides precisely shaped and timed radiation beams. Using pre-treatment scan data, as well as treatment planning and delivery software, the controller acquires information regarding the pre-treatment position and orientation of the treatment target region. The patient is usually placed on a support device, such as a couch or a table. During treatment, an imaging system repeatedly measures the position and orientation of the target relative to the x-ray source. Prior to the delivery of radiation at each delivery site, the controller directs the robot to adjust the position and orientation of the treatment beam generator, in accordance with the measurements made by imaging system, so that the requisite dose of the treatment beam can be applied to the treatment target within the patient.
FIG. 1 schematically illustrates one such radiotherapy system 10 described in U.S. Pat. No. 7,154,991 B2, entitled Patient Positioning Assembly For Therapeutic Radiation System, assigned to Accuray, Inc. This system 10 includes a robot 12 having an articulated arm assembly 13, a therapeutic radiation source 14 mounted at a distal end of the articulated arm assembly 13 for selectively emitting therapeutic radiation, an x-ray imaging system and a controller 18.
The x-ray imaging system generates image data representative of one or more near real time images of the target. The x-ray imaging system includes a pair of diagnostic x-ray sources 17, and a pair of x-ray image detectors (or cameras) 21, each detector located opposite an associated one of the x-ray sources 17. A patient support device (or treatment table) 19 supports the patient during treatment, and is positioned between the two x-ray cameras 21 and their respective diagnostic x-ray sources 17.
The imaging system generates, in near real time, x-ray images showing the position and orientation of the target in a treatment coordinate frame. The controller 18 contains treatment planning and delivery software, which is responsive to pre-treatment scan data CT (and/or MRI data and/or PET data and/or ultrasound scan data) and user input, to generate a treatment plan consisting of a succession of desired beam paths, each having an associated dose rate and duration at each of a fixed set of nodes.
Prior to performing a treatment on a patient, the patient's position and orientation within the frame of reference established by the x-ray imaging system must be adjusted to match the position and orientation that the patient had within the frame of reference of the CT (or MRI or PET) scanner that provided the images used for planning the treatment. It is desirable that this patient alignment be performed to within tenths of a millimeter and tenths of a degree for all six degrees of freedom.
Unfortunately, with such a mounted imaging system 10, the imaging views that are able to be taken are limited in orientation. Further, since the imaging system 10 is mounted, requiring two x-ray sources 17 and two cameras 21, the patient must be moved between the cameras 21 to image different parts or areas of the body. Any such movement of the table 19 once set up runs the risk of disturbing the alignment, i.e. patient's position and orientation, which will then need to be re-confirmed and set-up before further treatment is begun. Still further, such an imaging system 10 places constraints on the treatment envelope within the treatment room so as to avoid collisions between the table 19 and the cameras 21. These camera structures also take up, and therefore limit, the available space within the treatment room, obstructing free movement of the technician or other medical personnel when in the treatment room.
Additional radiotherapy systems are illustrated in U.S. Patent Publication Number 2007/0230660, entitled Medical Radiotherapy Assembly, by Klaus Herrmann. The '660 publication illustrates a first system where the imaging system is mounted to the therapeutic radiation source such that the x-ray source and x-ray detector of the imaging system rotate only angularly about a longitudinal axis defined by the particle beam of the therapeutic radiation source.
Again, unfortunately, with this mounted imaging system arrangement, the imaging views that are able to be taken are limited in orientation to being angularly positioned about the particle beam. Therefore, it is impossible in this system to align the imaging system, namely the x-ray source and x-ray detector, with the direction of particle beam.
A second system is disclosed in the '660 publication that includes an imaging system including an x-ray source and x-ray detector mounted to a support arm that is C-or U-shaped. This C- or U-shaped allows the support arm to be open on one side. This support arm is mounted to a six axes robot.
While this arrangement permits some improved positioning of the imaging system over the previous systems, the imaging system of this radiotherapy system (i.e. both he x-ray source and the x-ray detector) the x-ray detector of the imaging system cannot be used to help align or check alignment of the particle beam relative to the target area. Particularly, the x-ray source of the imaging system would be in the way of a particle beam line x-ray source of the therapeutic radiation source.
Instead, if the alignment of the particle beam is to be checked prior to therapy, a secondary independent x-ray detector must be positioned in place of the x-ray detector of the imaging system to cooperate with a particle beam line x-ray image prior to initiating the therapy of the patient. Again, this unfortunately, requires additional set-up of another imaging device which inherently imports potential error in the alignment of the particle beam.
Further, to adjust the orientation of the imaging system relative to a patient, the entire support arm and robot must be moved relative about the patient. Unfortunately, rotating the entire support arm from the mounting point requires overcoming substantial rotational inertia due to the size and weight of the support arm and the moment arm created by offsetting the x-ray detector and x-ray source from the point of rotation of the support arm.